There are many illnesses and medical conditions for which thermal ablation is an appropriate and effective treatment. Such conditions include, but are not limited to, prostate disorders including cancer, uterine dysfunction such as menorrhagia, rectal polyps, rectal and colon cancers, throat and oral cancers, various types of tumors, esophageal disorders such as Barrett's esophagus, etc.
Thermal ablation is a general term that is used to describe the technique of heating tissue that is diseased, or otherwise in need of treatment, in order to destroy tissue, at least down to a certain depth, thereby eliminating the disease or disorder, or at least reducing the symptoms thereof. There are many devices on the market and in clinical trials which utilize different types of energy, including radiofrequency (RF) energy, microwave energy, and ultrasound energy, to perform thermal ablation. The goal for each of these devices is, of course, the same—tissue destruction by thermal coagulation.
For example, Neuwirth, et al, “The Endometrial Ablator: A New Instrument”, Obst. & Gyn., 1994, Vol. 83, No. 5, Part 1, 792–796, performed endometrial ablation using a dextrose-filled balloon device mounted at the end of a carrier catheter and including a heating element inside the balloon. The heating element is a resistive heating coil that is used to heat the fluid within the balloon, which in turn, heats the endometrial tissue that is in contact with the exterior balloon surface. Neuwirth, et al. determined that if the surface of the balloon-tissue interface is maintained at about 90° C. for 7–12 minutes, the depth of damage to the endometrium was about 4–10 millimeters.
High frequency, or radiofrequency (RF), energy has been used to perform thermal ablation of endometrial tissue. For example, Prior, et al., “Treatment of Mennorrhagia By Radiofrequency Heating”, Int. J. Hyperthermia, 1991 Vol. 7, No. 2, 213–220, achieved a significant reduction in dysfunctional uterine bleeding using a device that includes a probe having a high frequency RF energy source that is inserted directly into the patient's uterus through the vagina and cervix. This energy source is an RF system having an electrode on the probe and a belt placed around the patient that serves as the return electrode. This RF system is operated at 27.12 MHz at a power of 550 Watts for about 20 minutes and achieves a deeper penetration than the Neuwirth, et al. device, which is an advantage over the Neuwirth, et al. device. However, this system suffers from the drawback that the location of the return electrode results in a scattering of the RF energy and less efficient delivery of the RF energy to the specific tissue to be treated.
U.S. Pat. No. 6,066,139 discloses a device that utilizes RF energy to perform transcervical sterilization by thermal ablation, as well as embolotherapy wherein the blood supply to tumors is reduced by sealing arterial feeder vessels. This device has two or more RF bipolar electrodes attached to the distal end of a catheter for delivery of RF energy for creating thermal lesions within the fallopian tubes that occlude the fallopian tube opening over time. While this device is generally successful at enabling the surgeon to manipulate the field of treatment, without the necessity of moving the catheter during the procedure, by selecting which combinations of electrodes are activated, there are still some limitations deriving from the unavoidable scattering of some of the RF energy and due to the fact that the RF energy travels only between the electrodes, which are located in fixed positions. Thus, this device fails to enable the surgeon to truly focus and refocus the energy emitted from the device on specific tissue areas during the surgical procedure. U.S. Pat. No. 6,066,139 also discloses an alternative embodiment wherein the RF electrodes are replaced with piezoelectric transducers and the device, therefore, emits ultrasound energy rather than RF energy.
A system marketed under the tradename THERMACHOICE®, by Ethicon, Inc. of Somerville, N.J., is currently used to perform thermal ablation of endometrial tissue. This system includes a latex balloon into which is circulated a heated dextrose and water solution. The balloon is attached to the distal end of a catheter carrier, through which the heated solution is circulated into the balloon, and the device often delivers satisfactory results. Some patients, however, present a need for deeper and broader endometrial penetration during ablation. In addition, it is noted that this device is particularly suited to thermal ablation of a relatively unfocused, broad tissue area, such as the inner tissue lining of a cavity or luminal structure and would not be suitable for focusing energy upon specific tissue areas.
U.S. Pat. No. 5,620,479 discloses a device for thermal treatment using ultrasound energy and having an array of tubular piezoelectric transducers disposed on a semi-flexible tubular carrier for delivering ultrasound energy directly to tissue to be ablated. The transducers are covered with a sealant coating and there is an outer covering over the sealant coating. U.S. Pat. No. 5,733,315 also discloses a device for ablating tissue using ultrasound energy that is adapted specifically for insertion into the rectum for treating the prostate. This device includes one or more ultrasound transducers disposed at least partly about a support tube, each ultrasound transducer having inactivated portions for reducing ultrasound energy directed to the rectal wall. The transducers of this device are also enclosed in a sealant.
U.S. Pat. No. 5,437,629 discloses an apparatus and method for recirculating heated fluid in the uterus to perform endometrial ablation, without using a balloon. U.S. Pat. No. 5,769,880 discloses an apparatus and method for performing thermal ablation, including endometrial tissue ablation, using bipolar RF energy. This device includes an electrode-carrying member mounted to the distal end of a shaft and an array of electrodes mounted to the surface of the electrode carrying member. A vacuum is utilized to draw out vapors, which are created when the tissue is ablated.
The foregoing devices and techniques all deliver energy in a general manner, without the ability to control or direct the application of energy in situ to the tissue to be treated. Lastly, the aforesaid devices are not designed to be movable during the time for which the energy source is activated, such that the emitted energy is redirected to particular tissue, thereby enabling a continuous treatment procedure.
The device of the present invention addresses the shortcomings of the existing apparatus and process for thermal ablation (especially endometrial ablation) by providing a device that delivers ultrasound energy to tissue to be treated in a controlled, focused and efficient manner. More particularly, the device has piezoelectric transducers that are mounted on one or more carriers such that transducers are movable, in situ during the treatment procedure, after initial positioning of the device and while the transducers are activated.